do i misunderstand something? the problem is that there is a new ebuild that should be upgraded, but one of the dependences is masked, so its impossible to upgrade. so the only way to make it work is to unmask the masked dependency - equal to using unstable packages.
in my case (-u sylpheed-claws) i can either wait until pgpme-3.10 becomes stable, or "make" pgpme-3.10 stable.

Calculating world dependencies /
!!! all ebuilds that could satisfy ">=sys-apps/groff-1.18" have been masked.
!!! (dependency required by "sys-apps/man-1.5k-r1" [ebuild])

I've tried to emerge portage 2.0.46, 2.0.47
and everything else in this thread,

Any suggestions? will this fix itself in some time?

I had this exact problem with man-1.5k-r1, and i also don't know what casues it. I did however add ACCEPT_KEYWORDS="~x86" to my make.conf as i was so graceously helped out https://forums.gentoo.org/viewtopic.php?t=29890here , and it seems to be a temporary fix for me, although i don't really like running unstable apps that much, especially the big ones (X glibc gcc and such). So now, i just weed out what upgrades i don't want when i upgrade. it takes way longer, but i still have my basic semi-stable system. I too hope this is fixed in the next portage/portage-tree. Good luck.

If one of the entries for the KEYWORDS in the suspect .ebuild file is "~x86" then the package is currently truley masked and should be emerged at ones own risk. I did have the other problem mentioned where "x86" not "~x86" was in the KEYWORDS varaible in the .ebuild which portage claimed was masked for me. "~alpha" was also in the ebuild. After fussing about I was able to get the package which depended on this to compile. I reccommed:

1) remove the ebuild file and emerge rsync
2) change any entries for KEYWORDS in the ebuild to non "~" which are not
"~x86" example: change "~sparc" to "sparc" if you're machine isn't a
sparc.
3) if "~x86" is not an entry for KEYWORDS in the ebuild, remove the entire
KEYWORDS line from the ebuild.
4) try adding the line
KEYWORDS="x86"
to your /etc/make.conf file